This invention relates to chemical vapor deposition (CVD) and particularly to the delivery to a CVD reaction chamber of copper precursor vapor from sources.
Chemical vapor deposition (CVD) processes such as those used in the manufacture of semiconductor devices require delivery of precursor vapor to a CVD reactor where a chemical reaction takes place that results in the deposition of a film on the semiconductor substrate. Increased demand for low resistivity contacts and interconnections has resulted in increased demand for commercial processes for depositing low loss metals such as copper, particularly for processes for forming contacts and interconnections on integrated circuits and semiconductor devices. CVD has provided a variety of processes for depositing copper as a metal for forming such integrated circuit connections.
In such CVD processes, precursors for copper are generally metal-organic liquids, most of which have very low vapor pressures. These low vapor pressure liquids must be vaporized for use in a CVD process. Such liquids, however, tend to be unstable at elevated temperatures and must be kept at or below room temperature up to the point of vaporization. The low vapor pressure of the precursors requires the vaporization chamber volume to be kept at a low pressure, in particular, at a pressure that is lower than the vapor pressure of the precursor at the vaporization temperature. Such requirements of low pressure and low temperature make it difficult to deliver the precursor vapor at a high rate and without degradation from a vaporization vessel to the reaction chamber where the CVD reaction is to take place.
As copper and other similar liquid precursors become unstable at high temperatures when in liquid state, condensation of such precursors from a vapor state produces a condensate that is also unstable. While the condensates of more conventional precursors can be easily re-evaporated, condensates of precursors, such as metal-organic precursors of copper, rapidly decompose to form solid residue on the surfaces on which they condense. Also, unless temperatures are low, such precursors undergo heterogeneous reaction at the walls of the vaporization chamber.
Many vaporizers have been made available for relatively stable, high vapor pressure precursors such as water and petroleum distillates. None, however, meets the requirements for delivering the low vapor pressure, low stability metal-organic precursors most suitable for copper CVD in semiconductor and integrated circuit manufacture.
Accordingly, there is a need for a better apparatus and method for delivery of reaction precursor vapor, particularly a vapor of a precursor having the characteristics of a metal-organic precursor of copper, to a CVD reaction chamber.
An objective of the present invention is to provide a precursor delivery system effective for reliably delivering vapor of low vapor pressure, low stability liquid precursors to a CVD chamber. A particular objective of the present invention is to deliver, from a metal-organic, particularly copper-organic, liquid precursor source, a vapor of the copper-organic or other metal-organic compound.
A further objective of the present invention is to deliver precursor vapor without decomposition of low stability, low vapor pressure precursor compounds. An additional objective is to deliver the precursor vapor without condensing the vapor in the apparatus after vaporization begins.
In accordance with certain principles of the present invention, a precursor delivery system is provided having an isothermal, high flow-conductance vaporizer that is directly integrated onto a CVD chamber. The system preferably includes a flow regulation of the liquid precursor to a high conductance vaporizer. The vaporizer is preferably configured to provide uniform thermal input to the precursor to promote efficient and repeatable vaporization. The high flow-conductance is provided which uniformly vaporizes low vapor pressure precursor liquids. The liquid remains at room temperature before vaporization, maintaining precursor liquid stability.
By xe2x80x9cisothermalxe2x80x9d is meant that heat is added to the precursor as it expands and is diffused into the reactor so that it neither condenses, deposits nor reacts upon entering the reactor. Otherwise, it is not necessary that the temperature of the precursor entering the reactor be held exactly constant. For copper-organic precursors, a temperature of between 60xc2x0 C. and 90xc2x0 C. is maintained. Further, by xe2x80x9chigh flow-conductancexe2x80x9d is meant that low resistance is provided to the flow of the precursor into the reactor, thereby not impeding the flow and causing minimal pressure drop entering the reactor, which lessens the pressure required at the precursor source.
In accordance with preferred embodiments of the invention, a CVD processing apparatus is provided with a precursor delivery system in which liquid precursor is metered into an atomizing orifice. The metering may be carried out with a conventional metering device or other device adapted to maintain the precursor, while in a liquid state, at or below room temperature or below such other temperature at which the precursor becomes unstable or is otherwise likely to degrade.
Further, an inert gas is used as a xe2x80x9csweep gasxe2x80x9d, and is introduced at the atomizer at the point of vaporization of the precursor to xe2x80x9csweepxe2x80x9d the atomized liquid into the vaporization chamber or volume at one end of a CVD reactor chamber. The vaporization volume is configured to provide an isothermal environment in which atomized liquid particles vaporize. The temperature of the vaporization volume is maintained high enough to prevent condensation of liquid onto walls and other structure in communication with the vaporization volume.
The sweep gas may simply be used to transport the gas into the reactor or it may be used to help atomize the liquid precursor droplets. To atomize the droplets, a heating of the sweep gas may be carried out. Such heating of the sweep gas can also serve as a way to add heat to the expanding gas, thereby facilitating the isothermal property of the delivery system.
In the certain embodiments of the invention, a low pressure environment is provided in the vaporization volume with a high vacuum conductance path maintained through the vaporization volume and into the CVD processing chamber.
The pressure of the liquid precursor into the atomizer is the pressure necessary to produce a flow rate in the range of from approximately 500 microliters per minute, plus or minus 100 xcexcl/min, to approximately 10 milli-liters per minute.
In accordance with the preferred embodiment of the invention, liquid copper-organic precursor is introduced directly at one end of a CVD processing chamber while maintaining the precursor, while in liquid state, at or below room temperature. The liquid precursor is atomized, preferably with the assistance of an inert sweep gas such as argon, and caused to flow through a vaporizer that is designed to present a progressively expanding volume, with the atomized precursor being subjected to uniform heating as it flows through the vaporizer. The vaporizer may be a series of concentric cylinders or concentric rings of passages of progressively increasing cross-section having conductive walls for conducting heat to the vapor as it expands. Alternatively, radiant heat may be used to maintain the temperature of the expanding vapor precursor. The precursor vapor preferably passes into a diffuser in which it expands to the low density of the gas in the CVD reaction chamber. The vapor may further optionally pass through a showerhead, which provides an additional pressure drop which allows for adaptation of the delivery system to different process parameters. Where such adaptation is not needed, it is preferred that the showerhead be omitted to minimize the pressure drop during precursor delivery.
Other objectives and advantages of the present invention will be readily apparent from the following detailed description of the present invention in which: